CN114262621B - Waste plastic liquefaction pyrolysis system and method - Google Patents
Waste plastic liquefaction pyrolysis system and method Download PDFInfo
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Abstract
A waste plastic liquefaction pyrolysis system and a method thereof, wherein a pretreatment system is used for processing waste plastic raw materials; the liquid phase tank heats and melts the waste plastic raw material, the treated liquid phase enters a multi-stage liquid cyclone through an outlet of the liquefaction tank, solid phase is discharged, and gas phase is sent to an oil-water separation system; the multistage liquid cyclone is used for solid-liquid separation, liquid phase discharged from the multistage liquid cyclone enters a buffer tank for temporary storage through the liquid phase, then is conveyed to an inlet of the plastic pyrolysis system through a conveying pump, and high-temperature pyrolysis oil gas generated by waste plastic pyrolysis enters an oil-water separation system; high-temperature flue gas generated by pyrolyzing waste plastics enters a waste heat recovery system; the oil-water separation system separates high-temperature pyrolysis oil gas and a gas phase entering the liquid phase tank, fuel oil and nitrogen are separated, and separated cold nitrogen enters the waste heat recovery system; the waste heat recovery system is used for exchanging heat of the entering high-temperature flue gas and cold nitrogen gas to obtain high-temperature nitrogen gas which enters the liquefaction tank to be used as a heat source for plastic liquefaction; the flue gas after waste heat utilization is treated by a flue gas purification system and then is discharged after reaching standards.
Description
Technical Field
The invention belongs to the field of garbage treatment, and particularly relates to a waste plastic liquefaction pyrolysis system and a waste plastic liquefaction pyrolysis method.
Background
Plastics are one of the major inventions of human beings since the 20 th century, and with the rise of the plastics industry in the middle of the 20 th century, human beings have entered the plastics era. The application of plastic products is deep in every corner of society, from industrial production to clothes and eating houses, and the plastic products are ubiquitous. The rapid development of the plastic industry brings a series of social problems caused by waste plastics and garbage and waste plastics which people do not want to see. A large amount of waste plastics are continuously and cumulatively generated in countries all over the world every year, and great environmental pressure is brought to the human society.
Waste plastics can be classified into two types from the viewpoint of utilization: the plastic can be recycled by recycling renewable waste plastics with higher quality and single component through a recycling technology, and the other is waste and miscellaneous plastic which cannot be recycled, such as hybrid plastic which has been recycled for many times or is mixed in domestic garbage and has low sorting value and is disassembled industrially. The non-renewable waste and miscellaneous plastic treatment technology mainly comprises a landfill technology, an incineration technology, a thermochemical recovery technology and the like, but the landfill technology is laggard, the environmental damage is serious, the incineration technology has serious secondary pollution, and the resource utilization of waste plastics cannot be realized. With the development of society and the improvement of environmental protection requirements, the waste plastic thermochemical recovery technology has great development potential. No matter physical recovery or thermochemical recovery, the feeding process of plastic pretreatment has the problems of easy coking and blockage, incapability of continuous conveying, low energy utilization rate and the like.
Therefore, in order to address the pain and the difficulty in the utilization or treatment of plastics, there is a need to develop a waste plastic liquefaction treatment technology with good environmental friendliness, high efficiency, and economic and social benefits.
Disclosure of Invention
The technical problem solved by the invention is as follows: solves the problems of serious environmental pollution and low resource utilization rate of the existing waste plastic treatment technology, provides a liquefaction pyrolysis resource utilization technology of waste plastic continuous sealed feeding, and realizes the maximum utilization of waste plastic resources.
The technical scheme of the invention is as follows: a waste plastic liquefaction pyrolysis system comprises a pretreatment system, a liquefaction tank, a multi-stage liquid cyclone, a buffer tank, a liquid phase conveying pump, a liquid discharge pump, a plastic pyrolysis system, a waste heat recovery system, a flue gas purification system and an oil-water separation system;
the pretreatment system is used for crushing, screening and demetalization of waste plastic raw materials, and an outlet of the pretreatment system is connected with an inlet at the top of the liquefaction tank;
the liquid phase tank is used for receiving waste plastic raw materials conveyed by the pretreatment system and heating and melting the waste plastic raw materials, the processed liquid phase enters the multistage liquid cyclone through the outlet of the liquefaction tank through the liquid discharge pump, the solid phase is discharged from the solid phase outlet at the bottom of the liquefaction tank, and the gas phase is discharged from the upper part of the liquefaction tank and is conveyed to the oil-water separation system;
the multistage liquid cyclone is used for solid-liquid separation, liquid phase discharged by the multistage liquid cyclone enters a buffer tank for temporary storage through the liquid phase, then is conveyed to an inlet of a plastic pyrolysis system through a conveying pump, and high-temperature pyrolysis oil gas generated by waste plastic pyrolysis enters an oil-water separation system; high-temperature flue gas generated by pyrolyzing waste plastics enters a waste heat recovery system;
the oil-water separation system is used for separating high-temperature pyrolysis oil gas and a gas phase entering a liquid phase tank, separating out fuel oil and nitrogen, and enabling separated cold nitrogen to enter a waste heat recovery system;
the waste heat recovery system is used for exchanging heat of the entering high-temperature flue gas and the entering cold nitrogen to obtain high-temperature nitrogen, and the high-temperature nitrogen enters the liquefaction tank to be used as a heat source for plastic liquefaction; the flue gas after the waste heat utilization is treated by a flue gas purification system and then is discharged after reaching the standard.
Preferably, the liquefaction tank comprises a raw material receiving mechanism, a heat tracing and heat insulating mechanism, a tank body, a stirring mechanism, a discharging mechanism, a gas phase distribution plate and a slag scraping plate;
the raw material receiving mechanism is used for realizing continuous sealed conveying of raw materials; the tank body is divided into a drying section and a liquefying section from top to bottom from a heat transfer angle, wherein a gas phase distribution plate and a slag scraping plate are arranged in the liquefying section, and the slag scraping plate is tightly attached to the gas phase distribution plate and periodically rotates to scrape slag; the stirring mechanism is used for uniformly stirring the liquefied plastic below the liquefaction section; the heat-preservation heat tracing mechanism is arranged outside the tank body and used for keeping the temperature of the cylinder body of the liquefaction tank; the material discharge mechanism is a material discharge opening, is positioned at the bottom of the tank body and has a conical rotational flow structure, and when the material rotates under the stirring action, the purpose of primary solid-liquid separation is realized, so that solid mechanical impurities at the bottom of the liquefaction tank can be discharged conveniently; the high-temperature nitrogen is cooled after liquefying the raw materials in the liquefying section, the raw materials in the drying section are continuously dried upwards, the dried water vapor is carried out of the liquefying tank, the gas phase outlet is positioned at the upper part of the tank body, the liquid phase outlet is arranged at the middle lower part of the tank body, and the outlet is connected with the inlet of the multistage liquid cyclone.
Preferably, the heat-preservation heat tracing mechanism is used for keeping the temperature of the cylinder body of the liquefaction tank between 250 and 300 ℃, and the temperature of the liquefied raw material is reduced to below 150 ℃ in the liquefaction section by high-temperature nitrogen.
Preferably, the contact mode of the high-temperature nitrogen and the plastic raw materials in the liquefying tank is countercurrent contact, the nitrogen inlet is positioned at the bottom of the tank body, and the nitrogen outlet is arranged at the top of the tank body.
Preferably, the raw material receiving mechanism comprises an upper sealing plate and a lower sealing plate, and the continuous sealing feeding is realized by alternately switching.
Preferably, cold nitrogen entering the waste heat recovery system is supplemented by the outside to make up for loss in the system operation process.
Preferably, the raw material pretreatment system crushes the raw material to be below 80mm in size through a fine crusher, and primary magnetic separation sections are respectively arranged at the front and the rear of the fine crusher and used for sorting out metal products in the material.
A method for liquefying and pyrolyzing waste plastics is realized by the following steps:
step one, treating waste plastic raw materials to enable the water content of the waste plastic raw materials to be 20-40%;
step two, electrifying the waste plastic liquefaction pyrolysis system for work; feeding waste plastic raw materials into a pretreatment system for crushing and deironing, feeding the deironing materials into a liquefaction tank through a screw conveyor, and recycling metals obtained in the deironing process;
controlling a raw material receiving mechanism to realize sealed feeding, controlling the temperature of a heat tracing and heat insulating mechanism to reach 350-450 ℃, liquefying the material, and controlling the heat tracing temperature of the heat tracing and heat insulating mechanism to be kept at 250-300 ℃ after detecting the generation of high-temperature nitrogen; controlling the flow speed and flow of the high-temperature nitrogen according to process conditions, and controlling the post-pump output pressure of a liquid discharge pump by adjusting the motor power of the liquid discharge pump so as to meet the requirement that a feed mixture is pushed into a multistage liquid cyclone at a preset pressure; controlling a delivery pump to continuously feed materials to the plastic pyrolysis system according to a preset delivery flow;
in the whole treatment process, the stirring mechanism is controlled to work, and the slag scraping plate periodically rotates to scrape slag; and detecting whether the content of cold nitrogen in the waste heat recovery system meets the requirement in real time, and if not, supplying cold nitrogen from the outside so as to continuously work the waste plastic liquefaction pyrolysis system.
Preferably, the preset pressure is 0.06-0.1 MPa.
The delivery flow rates of the liquid discharge pump and the delivery pump are determined according to the scale of the treatment, and the preferred delivery flow rate is 2 to 15 tons/hour.
Compared with the prior art, the invention has the beneficial effects that:
(1) The high-temperature flue gas and the nitrogen gas of the system are used for heat exchange, and the high-temperature nitrogen gas after heat exchange is used as a heat source for plastic liquefaction, so that the high-efficiency utilization of system energy is realized, and the thermal efficiency of the system is high; in addition, the cold nitrogen after oil-water separation returns to the waste heat recovery system for cyclic utilization, so that nitrogen resources are saved, and the system is green and economical.
(2) The invention uses inert gas hot nitrogen as the heat source of plastic liquefaction, realizes effective heat transfer of gas-solid phase, and simultaneously improves the safety of the liquefaction process.
(3) The plastic liquefaction process has serious coking problem, and the liquefaction tank is internally provided with structures such as stirring, rotating scrapers, deslagging, external heat insulation and the like, so that the stable and continuous operation of the liquefaction process is ensured; in addition, a multi-stage liquid cyclone is arranged behind the flow of the liquefaction tank, the slag in the material is removed again, the stage number of the multi-stage liquid cyclone is determined according to the solid content of the material, and the cleanliness of the subsequent material is ensured.
(4) The temperature distribution of the flue gas in the liquefaction tank is utilized, a drying section and a liquefaction section are formed in the liquefaction tank, and most of moisture in the raw materials is also taken away while the gradient utilization of high-temperature nitrogen heat is realized.
(5) The waste plastics after liquefaction are stored in the buffer tank and keep a certain liquid level, and the feeding flow is controlled by the pumping way, so that the continuous feeding of the materials into the plastic pyrolysis system is really realized.
(6) The subsequent processes from the inlet of the liquefaction tank are closed processes, the whole system has good tightness, the oxygen insulation and closing effects of the reaction environment are ensured, and the generation of harmful substances such as dioxin in the plastic pyrolysis system is fundamentally avoided.
Drawings
FIG. 1 is a schematic structural diagram of a waste plastic liquefaction pyrolysis system and method according to the present invention;
fig. 2 (a) is a schematic structural view of a liquefaction tank according to the present invention;
FIG. 2 (b) is a top view of a gas distribution plate in a liquefied tank according to the present invention;
in the figure: the system comprises a pretreatment system 1, a liquefaction tank 2, a raw material receiving mechanism 2a, a heat tracing and heat preserving mechanism 2b, a tank body 2c, a stirring mechanism 2d, a discharging mechanism 2e, a gas-phase distribution plate 2f, a slag scraping plate 2g, a multistage liquid cyclone 3, a buffer tank 4, a liquid-phase delivery pump 5, a plastic pyrolysis system 6, a waste heat recovery system 7, a flue gas purification system 8 and an oil-water separation system 9.
Detailed Description
The invention is further illustrated by the following examples.
A waste plastic liquefaction pyrolysis system comprises a pretreatment system 1, a liquefaction tank 2, a multi-stage liquid cyclone 3, a buffer tank 4, a liquid phase conveying pump 5, a plastic pyrolysis system 6, a waste heat recovery system 7, a flue gas purification system 8, an oil-water separation system 9 and a liquid discharge pump 10;
the liquefaction tank 2 comprises a raw material receiving mechanism 2a, a heat tracing and heat insulating mechanism 2b, a tank body 2c, a stirring mechanism 2d, a discharging mechanism 2e, a gas phase distribution plate 2f and a slag scraping plate 2g;
the plastic raw materials from the waste plastic storage yard are sent to a pretreatment system 1, an outlet of the raw material pretreatment system 1 is connected with an inlet at the top of a liquefaction tank 2, a liquid phase is connected with an inlet of a multistage liquid cyclone 3 through an outlet of the liquefaction tank 2, a solid phase is discharged from a solid phase outlet at the bottom of the liquefaction tank 2, a gas phase is discharged from the upper part of the liquefaction tank 2 and sent to an oil-water separation system 9, the liquid phase discharged from an overflow port of the multistage liquid cyclone 3 enters a buffer tank 4 for temporary storage through the liquid phase and then is conveyed to an inlet of a plastic pyrolysis system 6 through a conveying pump 5, high-temperature pyrolysis oil gas generated by pyrolysis of waste plastics enters the oil-water separation system 9 to generate high-quality fuel oil, heat exchange is carried out between high-temperature flue gas and cold nitrogen in a waste heat recovery system 7 to obtain high-temperature nitrogen, the hot nitrogen enters the liquefaction tank 2 to serve as a heat source for plastic liquefaction, the nitrogen lost in the system operation process can be supplemented from the outside, and the flue gas after waste heat utilization is treated by a flue gas purification system 8 and then reaches the standard to be discharged.
The raw material pretreatment system 1 can be used for crushing, screening and deironing the raw materials, so that the follow-up raw materials have higher cleanliness; in addition, the size of the raw materials can be crushed to be below 80mm, so that the continuity of subsequent conveying is ensured; the process is characterized in that primary magnetic separation sections are respectively arranged at the front and the rear of a fine crusher to select metal products in materials, and the selected metals can be sold. The water content of the waste plastic is about 30% during crushing, and the crushed plastic enters the liquefaction tank 2 as a raw material of the liquefaction process.
The liquefaction tank 2 is used for receiving waste plastic raw materials conveyed by the pretreatment unit and heating and melting the waste plastic raw materials, a heat source for heating the waste plastics is high-temperature nitrogen from an outlet of the waste heat recovery system 7, the nitrogen lost in the operation process of the system can be supplemented by the outside, and the heat source for heating the nitrogen is high-temperature flue gas from the plastic pyrolysis system 6. The temperature range of the high-temperature nitrogen is 350-450 ℃, the nitrogen and the plastic raw materials are in countercurrent contact in the liquefaction tank 2, the nitrogen inlet is positioned at the bottom of the liquefaction tank 2, and the nitrogen outlet is arranged at the top of the liquefaction tank 2. The liquefaction tank 2 is provided with a raw material receiving mechanism 2a, a heat tracing and heat preserving mechanism 2b, a tank body 2c, a stirring mechanism 2d, a discharging mechanism 2e, a gas phase distribution plate 2f and a slag scraping plate 2g;
the raw material receiving mechanism 2a is provided with a double-partition plate sealing device to realize continuous sealed conveying of raw materials. The stirring mechanism 2d is positioned at the middle lower part of the liquefaction tank 2 and is used for uniformly stirring the liquefied plastics. The heat preservation heat tracing mechanism 2b is arranged outside the cylinder body of the liquefaction tank 2 and keeps the temperature of the cylinder body of the liquefaction tank at 250-300 ℃. The discharge mechanism 2e is a discharge port, is positioned at the bottom of the liquefaction tank 2 and is of a conical cyclone structure, so that the purpose of primary solid-liquid separation can be realized when the material rotates under the stirring action, and the discharge of solid mechanical impurities at the bottom of the liquefaction tank is facilitated. The middle part of the liquefaction tank 2 is provided with a gas phase distribution plate 2f and a slag scraping plate 2g, and the slag scraping plate 2g is tightly attached to the gas phase distribution plate 2f and carries out periodic rotation slag scraping. From the perspective of heat transfer, liquefaction jar 2 from top to bottom can be divided into drying section and liquefaction section, and high temperature nitrogen gas reduces to ~ 150 ℃ after the liquefaction section liquefies the raw materials, continues upwards to carry the raw materials and carry the vapor that dries out of the liquefaction jar, and gaseous phase discharge port is located liquefaction jar 2 upper portion, and the liquid phase export sets up in liquefaction jar 2 middle and lower part, and the export is connected with positive displacement pump 10 entry, and the export of positive displacement pump 10 is connected with multistage liquid swirler 3 entry.
As shown in fig. 1:
step one, raw materials conveyed from a waste plastic raw material storage yard enter a pretreatment system 1, the water content of the raw materials from the plastic storage yard is 20-40% (if the water content is not satisfied, the raw materials need to be dried in advance and the like), the raw materials contain 1-5% of non-organic components such as metals and the like, the plastic raw materials are continuously and quantitatively conveyed to a coarse crusher by a belt conveyor, a specific crusher device and firmware are selected, the particle size of the raw materials can be crushed to be below 80mm after the raw materials are crushed, the crushed materials enter a magnetic separator to be deironized, the deironized materials are conveyed to a liquefaction process by a screw conveyor, and the metals obtained in the deironing process are recycled.
Secondly, the material from the pretreatment system enters a liquefaction tank 2 for liquefaction treatment, as shown in figure 2, the liquefaction tank 2 comprises a raw material receiving mechanism 2a, a heat tracing and heat preserving mechanism 2b, a tank body 2c, a stirring mechanism 2d, a discharging mechanism 2e, a gas phase distribution plate 2f and a slag scraping plate 2g, the material continuously falls into the raw material receiving mechanism 2a, the raw material receiving mechanism 2a comprises an upper sealing plate and a lower sealing plate, and the continuous sealing feeding can be realized by alternately switching; the material falling from the raw material receiving mechanism 2a is in countercurrent contact with high-temperature nitrogen from the bottom, the temperature of the nitrogen is 350-450 ℃ (the temperature for primary liquefaction is provided by a heat tracing and heat preservation mechanism), the flow rate and the flow rate of the high-temperature nitrogen are adjustable according to process conditions (when the flow rate of a delivery pump is changed within the range of 2-15 tons/hour, the flow rate of the high-temperature nitrogen is adjusted within the range of 800-6000 cubic meters/hour), the high-temperature nitrogen is discharged from a nitrogen outlet at the top of the liquefaction tank 2 and goes to an oil-water separation system 9, the cold nitrogen after oil-water separation is sent to a waste heat recovery system 7 for recycling, the nitrogen consumed in the operation process of the system can be supplemented by the outside, the liquid phase is deposited at the bottom of the liquefaction tank 2 in a backflow manner, and a stirring mechanism 2d is arranged at the middle lower part of the liquefaction tank 2 to prevent liquid phase from layering, adhesion and coking; the liquid phase is discharged through an outlet arranged at the middle lower part of the liquefaction tank 2; the bottom of the liquefaction tank 2 is provided with a solid-phase discharge mechanism 2e for discharging solid impurities at the bottom of the tank body; a smoke distribution plate 2f and a slag scraping plate 2g are arranged in the middle of the liquefaction tank 2, a certain number of round holes are formed in the gas phase distribution plate 2f, gas-liquid heat transfer is facilitated, and the slag scraping plate 2g is tightly attached to the gas phase distribution plate 2f and carries out periodic rotating slag scraping; in addition, a layer of heat tracing and heat insulating mechanism 2b is arranged on the periphery of the liquefaction tank 2, the heat tracing temperature is 250-300 ℃, the material is prevented from coking on the inner wall, and the fluidity of the material is favorably kept.
And step three, the liquid phase material from the liquefaction tank 2 enters a multi-stage liquid cyclone 3, the external pressure (the pressure is ensured by regulating the motor power of a liquid discharge pump to control the output pressure after the pump) is used for pushing the feeding mixture into the cyclone 3 at a larger pressure (for example, 0.06-0.1 MPa), because the mixture moves along the tangential direction of the cyclone, the liquid is promoted to rotate along the cylinder wall, the centrifugal force on the particles in the outer cyclone is larger than the liquid resistance generated by the movement, and the particles can overcome the resistance to move towards the wall of the cyclone, so that the effect of separating from the surrounding liquid is achieved. The stage number of the cyclone is determined by the solid content of the liquid material, and when the solid content is larger, a multistage cyclone can be arranged for deslagging.
And step four, the material flowing out of the overflow outlet of the multistage liquid cyclone 3 enters a buffer tank 4, the buffer tank 4 keeps a certain liquid level and is provided with a heat tracing insulation structure, and the flowability of the material is ensured.
And step five, conveying the materials in the buffer tank 4 to an inlet of the plastic pyrolysis system 6, and controlling the conveying flow by adopting a pumping mode, thereby really realizing the continuous feeding of the materials into the plastic pyrolysis system 6 and greatly improving the operation stability of the plastic pyrolysis system 6.
And step six, the high-temperature pyrolysis oil gas generated by the plastic pyrolysis system 6 enters an oil-water separation system 9, the effects of dedusting, cooling, oil-gas separation, dehydration and the like of the high-temperature oil gas can be realized in the system, and the purified non-condensable gas is used as supplementary fuel and is fed into the plastic pyrolysis system 6. The high-temperature flue gas generated by the plastic pyrolysis system 6 exchanges heat with cold nitrogen gas, and is treated by the flue gas purification system 8 and then is discharged after reaching the standard.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make variations and modifications of the present invention without departing from the spirit and scope of the present invention by using the methods and technical contents disclosed above.
Claims (10)
1. A waste plastic liquefaction pyrolysis system is characterized by comprising a pretreatment system (1), a liquefaction tank (2), a multi-stage liquid cyclone (3), a buffer tank (4), a liquid phase conveying pump (5), a plastic pyrolysis system (6), a waste heat recovery system (7), a flue gas purification system (8), an oil-water separation system (9) and a liquid discharge pump (10);
the pretreatment system (1) is used for crushing, screening and metal removing treatment of waste plastic raw materials, and an outlet of the pretreatment system is connected with an inlet at the top of the liquefaction tank (2);
the liquefaction tank (2) is used for receiving waste plastic raw materials conveyed by the pretreatment system and heating and melting the waste plastic raw materials, processed liquid phase enters the multistage liquid cyclone (3) through an outlet of the liquefaction tank (2) through the liquid discharge pump (10), solid phase is discharged from a solid phase outlet at the bottom of the liquefaction tank (2), and gas phase is discharged from the upper part of the liquefaction tank (2) and is conveyed to the oil-water separation system (9);
the multistage liquid cyclone (3) is used for solid-liquid separation, liquid phase discharged by the multistage liquid cyclone enters a buffer tank (4) for temporary storage, then is conveyed to an inlet of a plastic pyrolysis system (6) through a liquid phase conveying pump (5), and high-temperature pyrolysis oil gas generated by waste plastic pyrolysis enters an oil-water separation system (9); high-temperature flue gas generated by pyrolyzing waste plastics enters a waste heat recovery system;
the oil-water separation system (9) is used for separating high-temperature pyrolysis oil gas and a gas phase from a liquefaction tank to separate out fuel oil and nitrogen, and the separated cold nitrogen enters a waste heat recovery system;
the waste heat recovery system is used for exchanging heat of the entering high-temperature flue gas and the entering cold nitrogen gas to obtain high-temperature nitrogen gas, and the high-temperature nitrogen gas enters the liquefaction tank (2) to be used as a heat source for plastic liquefaction; the flue gas after waste heat utilization is treated by a flue gas purification system (8) and then is discharged after reaching standards.
2. The system of claim 1, wherein: the liquefaction tank (2) comprises a raw material receiving mechanism (2 a), a heat tracing and heat insulating mechanism (2 b), a tank body (2 c), a stirring mechanism (2 d), a discharging mechanism (2 e), a gas phase distribution plate (2 f) and a slag scraping plate (2 g);
the raw material receiving mechanism (2 a) is used for realizing continuous sealed conveying of raw materials; the tank body is divided into a drying section and a liquefying section from top to bottom from the heat transfer angle, wherein a gas phase distribution plate (2 f) and a slag scraping plate (2 g) are arranged in the liquefying section, and the slag scraping plate (2 g) is tightly attached to the gas phase distribution plate (2 f) and is used for periodically rotating and scraping slag; the stirring mechanism (2 d) is used for uniformly stirring the liquefied plastics below the liquefaction section; the heat tracing and heat insulating mechanism (2 b) is arranged outside the tank body (2 c) and is used for keeping the temperature of the cylinder body of the liquefaction tank; the discharge mechanism (2 e) is a discharge port, is positioned at the bottom of the tank body (2 c), is of a conical rotational flow structure, is used for realizing the purpose of primary solid-liquid separation when the material rotates under the stirring action, and is beneficial to discharging solid mechanical impurities at the bottom of the liquefaction tank; the high-temperature nitrogen is cooled after liquefying the raw materials in the liquefying section, the raw materials in the drying section are continuously dried upwards, the dried water vapor is carried out of the liquefying tank, the gas phase outlet is positioned at the upper part of the tank body, the liquid phase outlet is arranged at the middle lower part of the tank body, and the outlet is connected with the inlet of the multistage liquid cyclone (3).
3. The system of claim 2, wherein: the heat tracing and heat insulating mechanism (2 b) is used for keeping the temperature of the cylinder body of the liquefaction tank to be 250-300 ℃, and the temperature of the liquefied raw material is reduced to be below 150 ℃ after the high-temperature nitrogen liquefies the raw material in the liquefaction section.
4. The system of claim 2, wherein: the high-temperature nitrogen and the plastic raw materials are in countercurrent contact in the liquefaction tank (2), the nitrogen inlet is positioned at the bottom of the tank body, and the nitrogen outlet is arranged at the top of the tank body.
5. The system of claim 2, wherein: the raw material receiving mechanism comprises an upper sealing plate and a lower sealing plate, and continuous sealing feeding is realized by an alternate switch.
6. The system of claim 1, wherein: the cold nitrogen entering the waste heat recovery system is supplemented by the outside to make up for the loss in the system operation process.
7. The system of claim 1, wherein: the pretreatment system crushes the raw materials to be below 80mm through a fine crusher, and primary magnetic separation sections are respectively arranged at the front and the rear of the fine crusher to sort out metal products in the materials.
8. A method for liquefying and pyrolyzing waste plastics is characterized by being realized by the following steps:
step one, treating waste plastic raw materials to enable the water content of the waste plastic raw materials to be 20-40%;
step two, the waste plastic liquefaction pyrolysis system of claim 2 is powered on for work; feeding the waste plastic raw material into a pretreatment system, crushing and deironing, feeding the deironized material into a liquefaction tank through a screw conveyor, and recycling the metal obtained in the deironing process;
thirdly, controlling the raw material receiving mechanism to realize sealed feeding, controlling the temperature of the heat tracing and heat insulating mechanism to reach 350-450 ℃, liquefying the material, and controlling the heat tracing temperature of the heat tracing and heat insulating mechanism to be kept at 250-300 ℃ after detecting the generation of high-temperature nitrogen; controlling the flow speed and flow of the high-temperature nitrogen according to process conditions, and controlling the post-pump output pressure of the liquid discharge pump by adjusting the motor power of the liquid discharge pump to meet the condition that a feed mixture is pushed into the multistage liquid cyclone at a preset pressure; controlling a liquid-phase delivery pump to continuously feed materials to the plastic pyrolysis system according to a preset delivery flow;
the stirring mechanism is controlled to work in the whole treatment process, and the slag scraping plate periodically rotates to scrape slag; and detecting whether the content of cold nitrogen in the waste heat recovery system meets the requirement in real time, and if not, supplying cold nitrogen from the outside so as to continuously work the waste plastic liquefaction pyrolysis system.
9. The method of claim 8, wherein: the preset pressure is 0.06-0.1 MPa.
10. The method of claim 8, wherein: the delivery flow rates of the liquid discharge pump and the liquid phase delivery pump are determined according to the treatment scale, and the delivery flow rate is 2 to 15 tons/hour.
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Citations (11)
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